Wireless communications, like cell phone, PDA, notebook, tablet PC, 3G cell phone and the like, have been an indispensable technology of life in the past few years. To achieve the requirement of wireless communication, the communication frequency band has to be multi-band and broadband. By the development of technology, the antenna is required to be small sized, simply structured and easily produced. Most ways for increasing the communication frequency band and the band width are to increase the amount of antenna or cover the operation frequency band by broadband antenna. The volume of the conventional antenna occupies a lot of circuit area, which is undoubtedly not adequate to the light wireless communication products nowadays. The conventional antenna for multiple input and multiple output mostly adopts to increase the distance between two antennas or dispose the antennas with different poles for enhancing the antenna isolation. Furthermore, there are ways of putting an isolation unit between the two antennas, like inserting the slot or monopole slot as a band reject filter between the two antennas or placing a band reject filter circuit between the feed ports of two antennas. Increasing the distance between the antennas cannot reduce the size of the antenna for multiple input and multiple output. Disposing antennas with different poles cannot get a symmetric diverse radiation pattern for serving as an omnidirectional radiation pattern capable of improving the dead spot problem. Inserting the band reject unit usually cannot maintain a good isolation degree when two antennas are very close, and the size cannot either reduce effectively. Placing the circuit causes a great increase on the fabrication cost and the fabrication difficulty. Generally, antennal isolation degree is explained as the receiving capability of the adjacent antennas when a power is sent from the antenna. In WLAN IEEE802.11n system, the adjacent antennas can transmit and receive at the same time. If the receiving capabilities of the adjacent antennas are high, the isolation degrees of the adjacent antennas are low. Namely, the signal actually has not been transmitted, but the system receives the signal instead. Consequently, the transmission is greatly reduced. On the other hand, if the receiving capabilities of the adjacent antennas are low, the isolation degrees of the adjacent antennas are high. Namely, the signal is completely transmitted by the two antennas, so that the transmission rate is greatly enhanced.
Referring to the Taiwan patent number 1317188 issued at Nov. 11, 2011, titled “antenna and antenna combination”, it discloses an antenna disposed on a circuit board. The circuit board includes a first surface and a second surface. The antenna includes a feeding portion, a radiating portion, a first auxiliary radiating body, and a second auxiliary radiating body. The feeding portion includes a first feeding section and a second feeding section which are respectively disposed on the first surface and the second surface. The radiating portion includes a first radiating body, a second radiating body, a third radiating body, and a fourth radiating body. The first radiating body and the second radiating body are disposed on the first surface and electrically connected with the first feeding section; the third radiating body and the fourth radiating body are disposed on the second surface and electrically connected with the second feeding section. The first auxiliary radiating body is disposed on the first surface and electrically connected with the first radiating body; the second auxiliary radiating body is disposed on the first surface and electrically connected with the second radiating body. Therefore, Taiwan patent number 1317188 provides an antenna combination with the effects of less area/dimension and better isolation degree.
However, the isolation degree of the conventional patent is not good enough such that has the problems of serious signal interference and bad signal quality.